1. Field of Invention
This invention relates to deformable mirrors. Specifically, the present invention relates to large stroke deformable mirrors.
2. Description of the Related Art
Deformable mirrors are used in a variety of demanding applications including telescopes, infrared detectors, and spacecraft remote sensing devices. Such applications often demand mirrors with excellent optical qualities, durability, large stroke or range of movement, and heat exchange capability.
Historically, to achieve the required heat exchange capability, two plates of similar material were joined. The use of similar material for the front plate, and the backplate facilitated bonding the plates together. One plate was grooved, so that when the plates were joined, ducts would be formed at the interface between the two plates. These ducts would then be filled with circulating water or other fluid to carry away excess heat from the mirror and reduce temperature related mirror distortions.
To achieve optimal optical qualities, materials such as silicon or BK-7 were used. Although these materials provided excellent optical qualities, they lacked sufficient ductility and other mechanical properties required for long life of the mirror and large mirror stroke. In addition, large stresses at the points on the backplate connected to actuators and internal stresses and tensions between the two plates led to shortened mirror life.
To obtain large stroke, and long life from the mirrors, metal mirrors were implemented. Metal mirrors had the ductility but lacked sufficient optical qualities and low internal stresses.
In an effort to find a material that was durable with a large stroke and excellent optical qualities, a material called SUPER INVAR 36 percent nickel alloy with a low coefficient of thermal expansion was tested. In accordance with conventional fabrication techniques, SUPER INVAR alloy was used to fabricate the faceplate and the backplate of the mirror. When the faceplate was polished to achieve the desired optical properties, heat generated from polishing of the material changed the internal stresses and induced distortions in the mirror which impaired the optical performance thereof.
Hence, a need exists in the art for a mirror with improved durability, stable optical qualities, sufficient mechanical properties to withstand large deflections, and good heat exchange capability.